This invention relates to a PTC device formed integrally on a PCB substrate, such PCB substrate, a secondary battery protection circuit device wherein a secondary battery control circuit is provided on the substrate to control the temperature, voltage, and current of the secondary battery, and a secondary battery assembly provided with said device.
Various types of secondary batteries have in recent times been developed, such as nickel hydride batteries and lithium batteries. These are more lightweight and have a larger capacity than lead storage batteries conventionally used for electric power, and have been used in many applications. Because of their characteristics of light weight and large capacity, they have been used in electric vehicles powered by an electric motor and in hybrid vehicles, which combine an electric motor and an internal combustion engine.
Also, since the maximum voltage and current capacity in individual secondary batteries are limited by their reaction principle, a plurality of batteries are connected in series to obtain the required voltage for applications requiring a large driving force such as those described above, and the batteries are further connected in parallel to obtain the required current capacity.
When using such secondary batteries as are described above, the batteries must first be charged. Normally, the voltage required to charge the batteries is applied to the plurality of secondary batteries connected in series. However, this has a drawback as described below.
Notwithstanding the strictest quality control, it is difficult to achieve uniformity in the charge and discharge characteristics of the secondary batteries, and discrepancies in internal resistance, which change depending on the charge or discharge conditions, cannot be avoided. Thus, when a charge voltage is applied to the entirety of a plurality of secondary batteries having differing internal resistance and which are connected in series, the receiving current runs uniformly through all the batteries causing, in some cases, extreme temperature rises in secondary batteries having a high internal resistance. Not only will such temperature rises in a secondary battery shorten the life of the battery, but also in some cases the extreme temperature rise may damage the casing.
In order to eliminate such a drawback, the required voltage may be applied to both ends of each individual secondary battery while at the same time controlling overcurrents and overvoltages that may be applied to the secondary battery. Excessive temperature rises as described above must also be detected.
To achieve this, one method of detecting temperature rises is, for example, a bimetal contact method. In this method, however, if chattering occurs on the contacts through on-off switching, arc discharges may cause the contacts to stick together so that they no longer function as a switch. This method also had a problem with safety.
A method using PTC (Positive Temperature Coefficient) material having positive temperature coefficient characteristics to detect temperature in secondary batteries has also heretofore been used. When the surface temperature of the object to be measured is transmitted through contact, the PTC material shows a characteristic wherein it has a low electrical resistance at relatively low temperatures such as room temperature, but exhibits an extremely high resistance when exposed to a high temperature such as might occur when an abnormally large current flows through the object to be measured.
Specifically, control of such an overvoltage was conventionally performed by electronic components such as IC/LSIs and the like provided on a PCB substrate for that purpose, while detection of an overcurrent and an excessive temperature rise were performed by separate devices using circuits provided with PTC devices as described above.
This invention was devised in view of such circumstances and is intended to provide a PTC device formed integrally on a PCB substrate so that the electrode section on the substrate can be used as the outlet electrode, which takes up little space and which promotes efficiency by sharing part of its structure with the substrate. The invention is also intended to provide such a PCB substrate, a secondary battery protection circuit wherein current and voltage control circuits are both provided on said PCB substrate to improve the space factor of the circuit as a whole when compared with the use of discrete devices and to achieve energy savings, and a secondary battery assembly that includes this secondary battery protection circuit to allow comprehensive control of temperature, current, and voltage.
The invention is a PTC device exhibiting positive temperature coefficient behavior and having a pair of outlet electrodes formed integrally on the surface of said device, wherein at least one of said pair of outlet electrodes is an electrode section formed on a PCB substrate on which are mounted said PTC device and other electronic components such as a field effect transistor, semiconductor integrated circuit, and the like.
The invention is a PCB substrate on which is mounted a PTC device.
The invention is a secondary battery protection circuit device provided with a temperature detecting circuit for secondary batteries using the abovementioned PTC device, and a control circuit to control the current and voltage of the secondary batteries on the PCB substrate.
The invention is a secondary battery assembly provided with the secondary battery protection circuit device.
As explained above, according to this invention of a PTC device formed integrally on a PCB substrate, such a PCB substrate, a secondary battery protection circuit device comprising such PCB substrate provided with a circuit to control the voltage and current of secondary batteries, and a secondary battery assembly provided with said device, the following effects are obtained:
1. By using the electrode section of the PCB substrate as at least one of the outlet electrodes of the PTC device mounted on the PCB substrate, a space saving for the PCB substrate as a whole including the PTC device is achieved; also the manufacturing efficiency of the PCB substrate as a whole is improved and a high reliability is obtained.
2. Having a combination of PTC device and voltage/current control circuit on a single PCB substrate allows the temperature, voltage, and current of a secondary battery to be integrally controlled to protect the secondary battery.
3. By providing, together with the secondary battery, a secondary battery protection circuit device mounted on the above PCB substrate according to the invention, the volume of the secondary battery assembly is decreased, a cost reduction is achieved, and the reliability of temperature, voltage, and current control is improved.